The present invention relates to an optical disk permitting reading and writing of data while being rotated at a constant angular velocity, and more particularly to an optical disk having a recording surface divided into a plurality of zones, with clocks of higher frequencies being used for the access to the more outward zones so that the recording linear density is substantially identical between the outer and inner zones.
The present invention also relates to an optical disk which contains different types of recording media for the respective zones, and in which the types of the respective zones can be altered during use of the disk.
The present invention also relates to an optical disk drive device used for writing in and reading from the above-mentioned optical disks.
Known optical disks of the type having a storage capacity of 1 GB on each surface have a format proposed in ECMA/TC31/92/36. According to this proposal, the recording surface of the optical disk is divided into a plurality of zones equally, i.e. such that the numbers of the physical tracks in the respective zones are substantially equal. The number of zones depends on the size of the sector. If each sector consists of 512 bytes, the number of zones is 54. If each sector consists of 1024 bytes, the number of the zones is 30.
Each physical track has an integer number of sectors. The number of sectors in each track is constant throughout each zone. The number of sectors in each track is larger in more outward zones.
The optical disks that are available are either those of the R/W (read/write or rewritable) type which permit writing and rewriting as desired, and those of the WO (write-once) type which permit writing only once after fabrication, and those of O-ROM (embossed) type in which data is written at the time of fabrication, by embossing, and which do not permit writing after fabrication.
The number of sectors in each physical track differs from one zone to another, as described above. A complex algorithm is needed for indexing the physical location of the target sector when for instance the optical disk is used as a SCSI device, and is supplied with linear (consecutive integer-numbered) logical addresses. Moreover, the data field in each sector in an innermost physical track of a certain zone and the header field in each sector in an outermost physical track of another zone next to and inside of the first-mentioned zone may be adjacent to each other, with the result that the crosstalk from the header field may degrade the quality of the data read From the data field. This is because the information in the header field is written in the form of pit (embossment) and has a greater degree of modulation, causing a greater crosstalk, while the information in the data field is magneto-optically written and has a smaller degree of modulation. In this connection, it is noted that within each zone, header fields in all the tracks are radially aligned and data fields in all the tracks are radially aligned, so that a header field and a data field will not be adjacent to each other.
It is also desired that recording areas of the R/W type, of the WO type and of the O-ROM type be co-existing in a single disk to expand the application of the disks. In the past, optical disks of the P-ROM type, in which the recording areas of the R/W type and the recording areas of the O-ROM type are coexisting, were available. But, no other combination of recording areas have been known.